Safa Charfeddine

Investigation of the response to salinity and to oxidative stress of interspecific potato somatic hybrids grown in a greenhouse

AbstractSalinity is one of the major stresses threatening potato plants (Solanum tuberosum L.) by affecting their growth and yield. It leads to oxidative stress by the production of reactive oxygen species responsible for alteration of macromolecules. To improve the tolerance of potato to salt stress, we have used somatic hybridization to produce interspecific potato hybrids by protoplast fusion between the BF15 variety and the wild Solanum berthaultii species. These hybrids showed an improved tolerance to salt stress when cultivated in vitro. The present work aims to analyze the response of the hybrids to salt stress in greenhouse conditions. Thus, the development of plants and their antioxidant capacity in response to salt stress were followed. All hybrids showed better growth and stable chlorophyll content compared to those of the BF15 parent plant. Membrane lipid peroxidation, evaluated by measuring the malondialdehyde accumulation (MDA) in plant organs, showed low levels in the hybrids. Higher antioxidant enzyme activities were measured in the roots of the hybrids when compared to those of the BF15 parent. These hybrids also showed an improved control of Na+ accumulation and a stable K+/Na+ ratio. These results therefore confirm the better tolerance of these hybrids to salt stress when compared to their BF15 parent.

Genome-Wide Analysis and Expression Profiling of the ERF Transcription Factor Family in Potato (Solanum tuberosum L.)

The ERF transcription factors belong to the AP2/ERF superfamily, one of the largest transcription factor families in plants. They play important roles in plant development processes, as well as in the response to biotic, abiotic, and hormone signaling. In the present study, 155 putative ERF transcription factor genes were identified from the potato (Solanum tuberosum) genome database, and compared with those from Arabidopsis thaliana. The StERF proteins are divided into ten phylogenetic groups. Expression analyses of five StERFs were carried out by semi-quantitative RT-PCR and compared with published RNA-seq data. These latter analyses were used to distinguish tissue-specific, biotic, and abiotic stress genes as well as hormone-responsive StERF genes. The results are of interest to better understand the role of the AP2/ERF genes in response to diverse types of stress in potatoes. A comprehensive analysis of the physiological functions and biological roles of the ERF family genes in S. tuberosum is required to understand crop stress tolerance mechanisms.

Genome-wide identification and expression profiling of the late embryogenesis abundant genes in potato with emphasis on dehydrins

Late embryogenesis abundant (LEA) proteins were first described as accumulating late in plant seed development. They were also shown to be involved in plant responses to environmental stress and as well as in bacteria, yeast and invertebrates. They are known to play crucial roles in dehydration tolerance. This study describes a genome-wide analysis of LEA proteins and the corresponding genes in Solanum tuberosum. Twenty-nine LEA family members encoding genes in the Solanum genome were identified. Phylogenetic analyses allowed the classification of the potato LEA proteins into nine distinct groups. Some of them were identified as putative orthologs of Arabidopsis and rice LEA genes. In silico analyses confirmed the hydrophilicity of most of the StLEA proteins, whereas some of them can be folded. The in silico expression analyses showed that the identified genes displayed tissue-specific, stress and hormone-responsive expression profiles. Five StLEA classified as dehydrins were selected for expression analyses under salt and drought stresses. The data revealed that they were induced by both stresses. The analyses indicate that several factors such us developmental stages, hormones, and dehydration, can regulate the expression and activities of LEA protein. This report can be helpful for the further functional diversity studies and analyses of LEA proteins in potato. These genes can be overexpressed to improve potato abiotic stress response.

Identification and functional characterization of ten AP2/ERF genes in potato

Ethylene-responsive element-binding factors (ERF) constitute one of the largest transcription factor families in plants. In this study, we describe the cloning and the characterization of ten cDNAs encoding ERF factors from potato. The alignment of their AP2/ERF (Apetala2/ethylene-responsive factor) domain led to the identification of six StERFs (Solanum tuberosum ERFs) and four StDREBs (dehydration responsive element binding). The phylogeny and the sequence characterization allowed the classification of these StERFs into five ERF families. Expression analysis by semi-quantitative RT-PCR of these genes revealed that most of them are induced by hormone treatment such as abscisic acid, ethephon, jasmonic acid and salicylic acid. However, salt stress induced the expression of all StDREB but only three StERF genes. These results suggest that these transcription factors are involved in salt stress response. The StDREB1 and StDREB2 genes showed strong increase in expression in response to drought stress. In an attempt to improve drought tolerance in potato, we overexpressed StDREB1 and StDREB2 in transgenic potato plants (S. tuberosum L. Group Tuberosum) cv. Belle de Fontenay (BF15) and Spunta, respectively. The level of drought tolerance of these transgenic lines was significantly greater than that of wild-type control plants as measured by relative water content H2O2 content, free proline and total soluble sugars. The results suggest that the StDREB1 and StDREB2 as AP2/ERF transcription factors may play dual roles in response to drought stress in potato.

Potato dehydrins present high intrinsic disorder and are differentially expressed under ABA and abiotic stresses

Dehydrins (DHNs) correspond to late embryogenesis abundant proteins (LEA) of group 2, they are known as glycin rich proteins. Despite their expression during the late seed maturation stages, they are also involved in plant response to a number of abiotic stresses such as drought, salinity and cold. In the present study, we identified five full-length cDNAs encoding dehydrins (designated StDHN2a, StDHN1, TAS14, StDHN25 and StLEA27) isolated from potato. These dehydrins were composed of serine amino acids called S domain and lysine-rich segment corresponding to a K domain. Three DHNs (StDHN1, TAS14 and StLEA27) contained Y segments. In silico analysis showed that these StDHN sequences share high homology with other Solanum dehydrin proteins species. The analysis of gene expression using quantitative RT-PCR showed that they were upregulated by dehydration and salinity. Moreover, the search for putative regulatory element in the promoter sequence of dehydrin genes was investigated.

The StDREB1 transcription factor is involved in oxidative stress response and enhances tolerance to salt stress

We have shown previously that the potato dehydration responsive element binding (StDREB1) transcription factor plays an important role in regulating and improving salt and drought stress-response genes in potato plant. To further characterize StDREB1 involvement in stress response, we focuse here on the investigation of the StDREB1 target genes by an Electrophoretic mobility shift assay. The data obtains indicated that the StDREB1 protein can bind to both GCC and DRE boxes in the promoter sequence of target genes, suggesting that this transcription factor may play a key role in the response to abiotic- and biotic-stresses by the activation of the DRE- and GCC- mediated signaling pathways. In a second step, since some DREB factors were related to the oxidative stress response, we showed that H2O2 treatment led to a significant increase of StDREB1 expression in wild- type potato plants. Moreover, the analysis of the oxidative stress response of StDREB1 transgenic potato plants revealed lower levels of H2O2 and malondialdehyde than wild-type control plants submitted in vitro to salt stress. An increase in the antioxidant enzyme activities including superoxide dismutase (SOD) and catalase was also observed in StDREB1 plants. In addition, an enhanced expression of the Cu/Zn SOD gene was noticed in these StDREB1 transgenic plants, cultivated under salt stress conditions. These results suggest that StDREB1 plays an essential role in the regulation of stress-response by regulating the oxidative stress response. The involvement of this transcription factor in the activation of osmoprotectant synthesis was also confirmed.

Overexpression of dehydration-responsive element-binding 1 protein (DREB1) in transgenic Solanum tuberosum enhances tolerance to biotic stress

Abstract Plant growth and productivity are greatly affected by environmental stresses such as dehydration, high salinity, low temperature and pathogen infection. Plant adaptation to these environmental stresses is controlled by cascades of molecular networks. The dehydration-responsive element-binding (DREB) transcription factors play an important role in the response of plants to environmental stresses by controlling the expression of many stress-related genes. They specifically interact with C-repeat/DRE (A/GCCGAC) sequences present in the promoter regions of target genes. One of the DREB1 cDNA was previously cloned and overexpressed in transgenic potato plants. These transgenic plants displayed an improved tolerance to high salinity and drought stresses. The StDREB1 factor belongs to A-4 group that seem to be involved in biotic stress response. This report investigates the effect of Fusarium solani infection on the StDREB1 transgenic lines. Since a number of pathogenesis-related (PR) proteins are considered as DREB1 target genes, the expression of PR2, PR9 and PR3 genes were tested under biotic stress conditions. The β-1,3-glucanase (PR2) was specifically induced upon infection, whereas the chitinase and the peroxydase were expressed constitutively. The data also show that high levels of DREB1 transcripts accumulated rapidly when wild-type and transgenic plants were infected by F. solani. DREB1 transgenic potato plants accumulated higher levels of pathogenesis-related gene transcripts, such as PR2. These results showed that StDREB1 plays an important role in response to fungal attack in potato.

The positive effect of phosphogypsum-supplemented composts on potato plant growth in the field and tuber yield

The production of phosphoric acid from phosphate rock leads to an industrial by-product called phosphogypsum (PG). One ton of phosphoric acid generates 5 tons of PG that is frequently stocked near the production units. Several attempts were made to test PG valorization via soil amendment because of its phosphate, sulphate and calcium content. In this study, the use of PG in composting was envisaged. Composts were produced by mixing olive oil wastes and spent coffee grounds. Two concentrations of PG, 10% (A10) and 30% (A30), were tested in composting substrate in addition to control compost without PG (AT). After 8 months of fermentation, the resulting composts were used in field experiments using nine different treatments conducted to evaluate the potential use of these PG-containing composts in potato plant (cv. Spunta) cultivation. Plants were grown in the field and the different composts (AT, A10 and A30) were added as fertilizer and compared to commercial compost and cattle manure. During the culture period, a number of physiological (dry weight, chlorophyll content, tuber yield) and biochemical parameters (antioxidant activities, mineral content, starch and protein content) were followed. Similarly, chlorophyll content was measured in plants cultivated on commercial or PG supplemented composts. An increment of 55.17% in potato yield was recorded with the use of A30 the compost. Collectively, these data reveal the positive impact of the addition of PG in composting which may be adopted as a strategy for PG valorization and its use for the production of high quality edible products.